Electrode assemblies

ABSTRACT

Provided herein is electrode assembly for a nonaqueous electrolyte secondary battery, comprising at least one anode, at least one cathode and at least one separator interposed between the at least one anode and at least one cathode, wherein the at least one anode comprises an anode current collector and an anode electrode layer, and the at least one cathode comprises a cathode current collector and a cathode electrode layer, wherein each of the cathode and anode electrode layers independently has a void volume of less than 35%, and wherein each of the at least one cathode and anode independently has a peeling strength of 0.15 N/cm or more.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.15/272,521, filed on Sep. 22, 2016, which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates to the field of batteries. In particular,this invention relates to methods for drying electrode assemblies oflithium-ion batteries and electrode assemblies made by the methodsdisclosed herein.

BACKGROUND OF THE INVENTION

Lithium-ion batteries (LIBs) have attracted extensive attention in thepast two decades for a wide range of applications in portable electronicdevices such as cellular phones and laptop computers. Due to rapidmarket development of electric vehicles (EV) and grid energy storage,high-performance, low-cost LIBs are currently offering one of the mostpromising options for large-scale energy storage devices.

Currently, electrodes are prepared by dispersing fine powders of anactive battery electrode material, a conductive agent, and a bindermaterial in an appropriate solvent. The dispersion can be coated onto acurrent collector such as a copper or aluminum metal foil, and thendried at an elevated temperature to remove the solvent. Sheets of thecathode and anode are subsequently stacked or rolled with the separatorseparating the cathode and anode to form a battery.

The lithium-ion battery manufacturing process is sensitive to moisture.A battery with high water content leads to serious attenuation ofelectrochemical performance and affects stability of battery. Therefore,environmental humidity must be controlled strictly for the productionprocess of LIBs. Most of the LIBs are produced in an environment withless than 1 percent humidity. However, significant cost is incurredbecause of the stringent moisture-free process. To address the moisturesensitive issue of electrode assembly, it is important to dry theelectrode assembly prior to electrolyte filing so as to reduce the watercontent in the battery.

Chinese Patent No. 104142045 B describes a method of drying an electrodeassembly of LIBs. The method comprises heating an electrode assemblyunder vacuum at a temperature of 30-100° C.; filling the oven with dryair or inert gas; repeating these two steps for 1-10 times. This methodprovides the electrode assembly with a water content between 430.5 ppmand 488.1 ppm.

Chinese Patent Application No. 105115250 A describes a method of dryingan electrode assembly of LIBs. The method comprises heating an electrodeassembly under vacuum at a temperature of 85±5° C.; filling the ovenwith hot, dry nitrogen gas; repeating these two steps for 10-20 times.This method provides the electrode assembly with a water content of lessthan 200 ppm.

None of the above patent references discloses any binder composition inthe electrodes for evaluating the relationship between the dryingprofile and binder composition. In addition, the water contents of theelectrode assemblies as dried by the existing methods range from ahundred ppm to several hundreds ppm, which may affect the cyclingstability and rate capability of LIBs. Even if a battery is manufacturedusing the electrode obtained by the above method, exfoliation of anelectrode layer may occur and sufficient durability of the electrodelayer cannot be obtained.

JP Patent No. 5523678 B2 describes a positive electrode for a nonaqueouselectrolyte secondary battery, having a current collector and anelectrode layer containing an active material, a conductive agent and abinder, wherein the electrode layer has a percentage of void of 33.0% ormore to retain sufficient amount of electrolyte. However, the outputperformance will be affected due to decreased energy density of abattery. In addition, the peeling strength between the electrode layerand the current collector is determined by the surface roughness of thecurrent collector.

JP Patent No. 4984384 B2 describes a method for preparing an electrode,having a current collector and an active material layer containing aniron-containing active material and a binder. However, the peelingstrength between the active material layer and the current collector isalso determined by the surface roughness of the current collector.

In view of the above, there is always a need to provide a nonaqueouselectrolyte rechargeable battery using electrodes having high durabilityby inhibiting exfoliation of an electrode layer and good electrochemicalperformance.

SUMMARY OF THE INVENTION

The aforementioned needs are met by various aspects and embodimentsdisclosed herein.

In one aspect, provided herein is an electrode assembly for a nonaqueouselectrolyte secondary battery, comprising at least one anode, at leastone cathode and at least one separator interposed between the at leastone anode and at least one cathode, wherein the at least one anodecomprises an anode current collector and an anode electrode layer, andthe at least one cathode comprises a cathode current collector and acathode electrode layer, wherein each of the cathode and anode electrodelayers independently has a void volume of less than 35%, and whereineach of the at least one cathode and anode independently has a peelingstrength of 0.15 N/cm or more.

In some embodiments, the surface roughness of each of the cathode andanode current collectors is independently 2 μm or less, or 0.8 μm orless.

In certain embodiments, the density of each of the cathode and anodeelectrode layers is independently from about 1.0 g/cm³ to about 6.5g/cm³ or from about 1.0 g/cm³ to about 3.0 g/cm³.

In some embodiments, the thickness of each of the cathode and anodeelectrode layers is independently from about 1.0 μm to about 40 μm orfrom about 1.0 μm to about 25 μm.

In certain embodiments, the cathode electrode layer comprises a cathodematerial, a binder material and a conductive agent, and the anodeelectrode layer comprises an anode material, a binder material and aconductive agent, and wherein each of the binder materials in thecathode and anode electrode layers is independently selected from thegroup consisting of styrene-butadiene rubber, acrylatedstyrene-butadiene rubber, acrylonitrile copolymer,acrylonitrile-butadiene rubber, nitrile butadiene rubber,acrylonitrile-styrene-butadiene copolymer, acryl rubber, butyl rubber,fluorine rubber, polytetrafluoroethylene, polyethylene, polypropylene,ethylene/propylene copolymers, polybutadiene, polyethylene oxide,chlorosulfonated polyethylene, polyvinylpyrrolidone, polyvinylpyridine,polyvinyl alcohol, polyvinyl acetate, polyepichlorohydrin,polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resins,phenolic resins, epoxy resins, carboxymethyl cellulose, hydroxypropylcellulose, cellulose acetate, cellulose acetate butyrate, celluloseacetate propionate, cyanoethylcellulose, cyanoethylsucrose, polyester,polyamide, polyether, polyimide, polycarboxylate, polycarboxylic acid,polyacrylic acid, polyacrylate, polymethacrylic acid, polymethacrylate,polyacrylamide, polyurethane, fluorinated polymer, chlorinated polymer,a salt of alginic acid, polyvinylidene fluoride, poly(vinylidenefluoride)-hexafluoropropene, and combinations thereof.

In some embodiments, each of the binder materials in the cathode andanode electrode layers is independently present in an amount from 2% to10% by weight, based on the total weight of the cathode or anodeelectrode layer.

In certain embodiments, the cathode electrode layer comprises a cathodematerial selected from the group consisting of LiCoO₂, LiNiO₂,LiNi_(x)Mn_(y)O₂, Li_(1+z)Ni_(x)Mn_(y)Co_(1-x-y)O₂,LiNi_(x)Co_(y)Al_(z)O₂, LiV₂O₅, LiTiS₂, LiMoS₂, LiMnO₂, LiCrO₂, LiMn₂O₄,LiFeO₂, LiFePO₄, and combinations thereof, wherein each x isindependently from 0.3 to 0.8; each y is independently from 0.1 to 0.45;and each z is independently from 0 to 0.2.

In some embodiments, the cathode material is present in an amount from60% to 99% by weight, based on the total weight of the cathode electrodelayer.

In certain embodiments, the cathode electrode layer comprises a cathodematerial, a binder material and a conductive agent, and the anodeelectrode layer comprises an anode material, a binder material and aconductive agent, and wherein each of the conductive agents in thecathode and anode electrode layers is independently selected from thegroup consisting of carbon, carbon black, graphite, expanded graphite,graphene, graphene nanoplatelets, carbon fibres, carbon nano-fibers,graphitized carbon flake, carbon tubes, carbon nanotubes, activatedcarbon, mesoporous carbon, and combinations thereof.

In some embodiments, each of the conductive agents in the cathode andanode electrode layers is independently present in an amount from 2% to10% by weight, based on the total weight of the cathode or anodeelectrode layer.

In certain embodiments, the anode electrode layer comprises an anodematerial selected from the group consisting of natural graphiteparticulate, synthetic graphite particulate, Sn particulate, Li₄Ti₅O₁₂particulate, Si particulate, Si—C composite particulate, andcombinations thereof.

In some embodiments, the anode material is present in an amount from 50%to 99% by weight, based on the total weight of the anode electrodelayer.

In certain embodiments, each of the cathode and anode current collectorsis independently stainless steel, titanium, nickel, aluminum, copper, orelectrically-conductive resin. In some embodiments, the cathode currentcollector is an aluminum thin film, and the anode current collector is acopper thin film.

In some embodiments, the water content of the electrode assembly is lessthan 20 ppm, less than 10 ppm, or less than 5 ppm by weight, based onthe total weight of the electrode assembly.

In certain embodiments, the at least one anode and at least one cathodehave a water content of less than 20 ppm, less than 10 ppm, or less than5 ppm by weight, based on the total weight of the at least one anode andat least one cathode.

In some embodiments, the at least one separator has a water content ofless than 20 ppm, less than 10 ppm, or less than 5 ppm by weight, basedon the total weight of the at least one separator.

Also provided herein is a lithium-ion battery comprising the electrodeassembly prepared by the method disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts cycling performance of an electrochemical cell containingan electrode assembly prepared by the method described in Example 2.

FIG. 2 depicts cycling performance of an electrochemical cell containingan electrode assembly prepared by the method described in Example 4.

FIG. 3 depicts cycling performance of an electrochemical cell containingan electrode assembly prepared by the method described in Example 6.

FIG. 4 depicts cycling performance of an electrochemical cell containingan electrode assembly prepared by the method described in Example 8.

DETAILED DESCRIPTION OF THE INVENTION

Provided herein is an electrode assembly for a nonaqueous electrolytesecondary battery, comprising at least one anode, at least one cathodeand at least one separator interposed between the at least one anode andat least one cathode, wherein the at least one anode comprises an anodecurrent collector and an anode electrode layer, and the at least onecathode comprises a cathode current collector and a cathode electrodelayer, wherein each of the cathode and anode electrode layersindependently has a void volume of less than 35%, and wherein each ofthe at least one cathode and anode independently has a peeling strengthof 0.15 N/cm or more.

The term “electrode” refers to a “cathode” or an “anode.”

The term “positive electrode” is used interchangeably with cathode.Likewise, the term “negative electrode” is used interchangeably withanode.

The term “binder material” refers to a chemical or a substance that canbe used to hold the active battery electrode material and conductiveagent in place.

The term “water-based binder material” refers to a water-soluble orwater-dispersible binder polymer. Some non-limiting examples of thewater-based binder material include styrene-butadiene rubber, acrylatedstyrene-butadiene rubber, acrylonitrile-butadiene rubber, acryl rubber,butyl rubber, fluorine rubber, polytetrafluoroethylene, polyethylene,polypropylene, ethylene/propylene copolymers, polybutadiene,polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin,polyphosphazene, polyacrylonitrile, polystyrene,ethylene/propylene/diene copolymers, polyvinylpyridine, chlorosulfonatedpolyethylene, latex, polyester resins, acrylic resins, phenolic resins,epoxy resins, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropylcellulose, and combinations thereof.

The term “organic-based binder material” refers to a binder dissolved ordispersed in an organic solvent, in particular, N-methyl pyrrolidone(NMP). Some non-limiting examples of the organic-based binder materialinclude polytetrafluoroethylene (PTFE), perfluoroalkoxy polymer (PFA),polyvinylidene fluoride (PVDF), copolymer of tetrafluoroethylene (TFE)and hexafluoropropylene (HFP), fluorinated ethylene-propylene (FEP)copolymer, and terpolymer of tetrafluoroethylene, hexafluoropropyleneand vinylidene fluoride, and combinations thereof.

The term “current collector” refers to a support for coating the activebattery electrode material and a chemically inactive high electronconductor for keeping an electric current flowing to electrodes duringdischarging or charging a secondary battery.

The term “conductive agent” refers to a material which is chemicallyinactive and has good electrical conductivity. Therefore, the conductiveagent is often mixed with an electrode active material at the time offorming an electrode to improve electrical conductivity of theelectrode. In some embodiments, the conductive agent is a carbonaceousmaterial.

The term “electrode assembly” refers to a structure comprising at leastone positive electrode, at least one negative electrode, and at leastone separator interposed between the positive electrode and the negativeelectrode.

The term “peeling strength” refers to the force required to separate acoating layer from a substrate to which it has been laminated.

The term “surface roughness” refers to the irregularities of shapepresent on the surface of a material.

The term “room temperature” refers to indoor temperatures from about 18°C. to about 30° C., e.g., 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28,29, or 30° C. In some embodiments, room temperature refers to atemperature of about 20° C. +/−1° C. or +/−2° C. or +/−3° C. In otherembodiments, room temperature refers to a temperature of about 22° C. orabout 25° C.

The term “C rate” refers to the charging or discharging rate of a cellor battery, expressed in terms of its total storage capacity in Ah ormAh. For example, a rate of 1 C means utilization of all of the storedenergy in one hour; a 0.1 C means utilization of 10% of the energy inone hour or full energy in 10 hours; and a 5 C means utilization of fullenergy in 12 minutes.

The term “ampere-hour (Ah)” refers to a unit used in specifying thestorage capacity of a battery. For example, a battery with 1 Ah capacitycan supply a current of one ampere for one hour or 0.5 A for two hours,etc. Therefore, 1 Ampere-hour (Ah) is the equivalent of 3600 coulombs ofelectrical charge. Similarly, the term “miniampere-hour (mAh)” alsorefers to a unit of the storage capacity of a battery and is 1/1,000 ofan ampere-hour.

The term “battery cycle life” refers to the number of completecharge/discharge cycles a battery can perform before its nominalcapacity falls below 80% of its initial rated capacity.

In the following description, all numbers disclosed herein areapproximate values, regardless whether the word “about” or “approximate”is used in connection therewith. They may vary by 1 percent, 2 percent,5 percent, or, sometimes, 10 to 20 percent. Whenever a numerical rangewith a lower limit, R^(L), and an upper limit, R^(U), is disclosed, anynumber falling within the range is specifically disclosed. Inparticular, the following numbers within the range are specificallydisclosed: R=R^(L)+k*(R^(U)−R^(L)), wherein k is a variable ranging from1 percent to 100 percent with a 1 percent increment, i.e., k is 1percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . , 50 percent,51 percent, 52 percent, . . . , 95 percent, 96 percent, 97 percent, 98percent, 99 percent, or 100 percent. Moreover, any numerical rangedefined by two R numbers as defined in the above is also specificallydisclosed.

Generally, lithium-ion battery manufacturing processes are carried outin dry rooms where the environment must be carefully controlled topreserve optimum production conditions. The dew point of the air is anindicator of the quality of the dry room. Typical dew point values forbattery production range from −40° C. to −65° C. Efficiency and servicelife of a battery are determined in the cell production stage.Nevertheless, no prior art document describes a method for achieving anelectrode assembly having a particularly low water content (e.g. lessthan 20 ppm).

An electrode assembly can be constructed by sequentially stacking atleast one negative electrode, at least one separator, and at least onepositive electrode. The number and arrangement of the at least onepositive electrode, the at least one negative electrode, and the atleast one separator, for configuring the electrode assembly are notparticularly limited. In some embodiments, the electrode assembly has astacked structure in which two outermost electrodes comprise an opposingpolarities (i.e., a positive electrode and a negative electrode), suchas a positive electrode/separator/negative electrode structure or apositive electrode/separator/negative electrode/separator/positiveelectrode/separator/negative electrode structure.

In certain embodiments, the electrode assembly has a stacked structurein which two outermost electrodes comprise the same polarity (i.e.,positive electrodes or negative electrodes), such as a positiveelectrode/separator/negative electrode/separator/positive electrodestructure or a negative electrode/separator/positiveelectrode/separator/negative electrode structure.

In some embodiments, the electrode assembly has a structure in which aseparator is disposed on one of the outermost sides, such as aseparator/positive electrode/separator/negative electrode structure or apositive electrode/separator/negative electrode/separator structure. Inother embodiments, the electrode assembly has a structure in whichseparators are disposed on both the outermost sides, such as aseparator/positive electrode/separator/negative electrode/separatorstructure.

In certain embodiments, the electrode assembly is assembled under stricthumidity control in which the air has a dew point of −65° C. In someembodiments, the electrode assembly is assembled under dry conditions inwhich the air has a dew point of −50° C., −40° C., −30° C., −20° C.,−10° C., 0° C., 5° C., or 10° C. In certain embodiments, the electrodeassembly is assembled in the open air with no control of humidity.

The separator disposed between the opposing active anode and cathodesurfaces can prevent contact between the anode and cathode and a shortcircuit of the lithium ion battery. In some embodiments, the separatormay comprise woven or nonwoven polymeric fibers, natural fibers, carbonfibers, glass fibers or ceramic fibers. In certain embodiments, theseparator comprises woven or nonwoven polymeric fibers.

In certain embodiments, the fibers of the nonwoven or woven are made oforganic polymers, such as polyolefin, polyethylene, high-densitypolyethylene, linear low-density polyethylene, low-density polyethylene,ultrahigh-molecular-weight polyethylene, polypropylene,polypropylene/polyethylene co-polymer, polybutylene, polypentene,polyacetal, polyamide, polycarbonate, polyimide, polyetherether ketone,polysulfones, polyphenylene oxide, polyphenylene sulfide,polyacrylonitrile, polyvinylidene fluoride, polyoxymethylene, polyvinylpyrrolidone, polyester, polyethylene terephthalate, polybutyleneterephthalate, polyethylene naphthalene, polybutylene naphthalate,derivatives thereof, or a combination thereof. In certain embodiments,the separator is made of polyolefinic fibers selected from the groupconsisting of polyethylene, high-density polyethylene, linearlow-density polyethylene, low-density polyethylene,ultrahigh-molecular-weight polyethylene, polypropylene,polypropylene/polyethylene co-polymer, and combinations thereof. In someembodiments, the separator is made of polymeric fibers selected from thegroup consisting of polyester, polyacetal, polyamide, polycarbonate,polyimide, polyetherether ketone, polyether sulfone, polyphenyleneoxide, polyphenylene sulfide, polyethylene naphthalene, and combinationsthereof. In other embodiments, the polymeric fiber is not polyethylene,high-density polyethylene, linear low-density polyethylene, low-densitypolyethylene, ultrahigh-molecular-weight polyethylene, polypropylene, orpolypropylene/polyethylene co-polymer. In further embodiments, thepolymeric fiber is not polyacetal, polyether sulfone, polyphenyleneoxide, polyphenylene sulfide, or polycarbonate. In still furtherembodiments, polymeric fiber is not polyamide, polyimide, orpolyetherether ketone. But all other known polymeric fibers and manynatural fibers can be used as well.

In some embodiments, the separator disclosed herein has a melting pointof 100° C. or higher, 120° C. or higher, 140° C. or higher, 160° C. orhigher, 180° C. or higher, 200° C. or higher, or 250° C. or higher. Insome embodiments, the separator disclosed herein has a melting point of140° C. or higher, 160° C. or higher, 180° C. or higher, 200° C. orhigher, or 250° C. or higher. The separator having high melting pointshows high thermal stability and therefore can be dried at hightemperature without thermally shrinking. This also allows the drying tobe more efficiently performed. Therefore, the electrode assembly can bedried in a relatively short time, resulting in a short production time.

The separator can be in a coated or uncoated form. In some embodiments,the separator has a thickness from about 10 μm to about 200 μm, fromabout 30 μm to about 100 μm, from about 10 μm to about 75 μm, from about10 μm to about 50 μm, from about 10 μm to about 20 μm, from about 15 μmto about 40 μm, from about 15 μm to about 35 μm, from about 20 μm toabout 40 μm, from about 20 μm to about 35 μm, from about 20 μm to about30 μm, from about 30 μm to about 60 μm, from about 30 μm to about 50 μm,or from about 30 μm to about 40 μm.

In certain embodiments, the separator has a thickness of about 15 μm,about 20 μm, or about 25 μm. In some embodiments, the separator of thepresent invention has a thickness of less than 40 μm, less than 35 μm,less than 30 μm, less than 25 μm, or less than 20 μm. If the separatoris sufficiently thin, the moisture may be evaporated at high dryingrates.

In some embodiments, the electrode assembly is loosely stacked. In theloosely stacked electrode assembly, there is a void space between theelectrode layer and separator layer, allowing moisture to escape.Therefore, the loosely stacked electrode assembly can be effectivelydried in a short period of time. On the other hand, when the electrodeassembly is pressed under pressure before drying, the tightly packedelectrode assembly has little or no void space between the electrodelayer and separator layer, thus reducing airflow and drying efficiency.

In certain embodiments, the positive electrode, separator and negativeelectrode are stacked and spirally wound into a jelly-roll configurationbefore drying. Since a roll electrode assembly is tightly packed, thereis also little or no void space between the electrode layer andseparator layer, thus reducing airflow and drying efficiency.

A positive electrode includes a cathode electrode layer supported on acathode current collector. The cathode electrode layer comprises atleast a cathode material and a binder material. The cathode electrodelayer may further comprise a conductive agent for enhancing electronconductivity of the cathode electrode layer. A negative electrodeincludes an anode electrode layer supported on an anode currentcollector. The anode electrode layer comprises at least an anodematerial and a binder material. The anode electrode layer may furthercomprise a conductive agent for enhancing electron conductivity of theanode electrode layer.

In some embodiments, the at least one cathode comprises a cathodecurrent collector and a cathode electrode layer comprising a cathodematerial, a binder material and a conductive agent, and the at least oneanode comprises an anode current collector and an anode electrode layercomprising an anode material, a binder material and a conductive agent,wherein each of the cathode and anode electrode layers independently hasa void volume of less than 40%, less than 37%, less than 35%, less than33%, less than 30%, less than 25%, less than 20%, less than 18%, lessthan 15%, less than 13%, less than 10%, or less than 8%, based on thetotal volume of the cathode or anode electrode layer. In certainembodiments, the void volume of each of the cathode and anode electrodelayers is independently between 8% and 40%, between 8% and 35%, between8% and 30%, between 10% and 30%, between 13% and 30%, between 13% and33%, between 15% and 30%, between 18% and 30%, between 20% and 30%, orbetween 25% and 30%, based on the total volume of the cathode or anodeelectrode layer.

If the void volume of the electrode layer is 35% or more, both theenergy density and power output of the battery are low. When the voidvolume of the electrode layer is between 10% and 35%, the batteryexhibits good diffusibility of lithium ions and high-output performance.

The current collector acts to collect electrons generated byelectrochemical reactions of the active battery electrode material or tosupply electrons required for the electrochemical reactions. In someembodiments, each of the current collectors of the positive and negativeelectrodes, which can be in the form of a foil, sheet or film, isindependently stainless steel, titanium, nickel, aluminum, copper orelectrically-conductive resin. In certain embodiments, the cathodecurrent collector is an aluminum thin film. In some embodiments, theanode current collector is a copper thin film.

In some embodiments, the current collector has a thickness from about 6μm to about 100 μm. Thickness of the current collector will affect thevolume occupied by the current collector within a battery and the amountof the electrode material and hence the capacity in the battery.

A surface roughness formed on a surface of the current collector canenhance binding force of the electrode material to the currentcollector, improving adhesion between the current collector and theelectrode layer. In certain embodiments, the current collector has asurface roughness Ra from about 0.1 μm to about 5 μm, from about 1 μm toabout 3 μm, from about 0.1 μm to about 1 μm, or from about 0.1 μm toabout 0.5 μm. In some embodiments, the current collector has a surfaceroughness of 4 μm or less, 3 μm or less, 2 μm or less, 1.5 μm or less,0.8 μm or less, or 0.5 μm or less.

In some embodiments, the thickness of each of the cathode and anodeelectrode layers on the current collector is independently from about 1μm to about 300 μm, from about 10 μm to about 300 μm, from about 20 μmto about 100 μm, from about 1 μm to about 100 μm, from about 1 μm toabout 50 μm, from about 1 μm to about 40 μm, from about 10 μm to about40 μm, from about 10 μm to about 30 μm, or from about 10 μm to about 25μm. In some embodiments, the thickness of the electrode layer on thecurrent collector is about 10 μm, about 15 μm, about 20 μm, about 25 μm,about 30 μm, about 35 μm, or about 40 μm.

In certain embodiments, the density of each of the cathode and anodeelectrode layers on the current collector is independently from about1.0 g/cm³ to about 6.5 g/cm³, from about 1.0 g/cm³ to about 5.0 g/cm³,from about 1.0 g/cm³ to about 4.0 g/cm³, from about 1.0 g/cm³ to about3.5 g/cm³, from about 1.0 g/cm³ to about 3.0 g/cm³, from about 1.0 g/cm³to about 2.0 g/cm³, from about 2.0 g/cm³ to about 5.0 g/cm³, from about2.0 g/cm³ to about 4.0 g/cm³, from about 3.0 g/cm³ to about 5.0 g/cm³,or from about 3.0 g/cm³ to about 6.0 g/cm³. Similarly, an increase inthe density of the electrode layer will result in a reduction of voidvolume in the final electrode coating and a denser electrode, therebyachieving desired battery capacity.

In some embodiments, the cathode material is selected from the groupconsisting of LiCoO₂, LiNiO₂, LiNi_(x)Mn_(y)O₂,Li_(1+z)Ni_(x)Mn_(y)Co_(1-x-y)O₂, LiNi_(x)Co_(y)Al_(z)O₂, LiV₂O₅,LiTiS₂, LiMoS₂, LiMnO₂, LiCrO₂, LiMn₂O₄, LiFeO₂, LiFePO₄, andcombinations thereof, wherein each x is independently from 0.3 to 0.8;each y is independently from 0.1 to 0.45; and each z is independentlyfrom 0 to 0.2. In certain embodiments, the cathode material is selectedfrom the group consisting of LiCoO₂, LiNiO₂, LiNi_(x)Mn_(y)O₂,Li_(1+z)Ni_(x)Mn_(y)Co_(1-x-y)O₂, LiNi_(x)Co_(y)Al_(z)O₂, LiV₂O₅,LiTiS₂, LiMoS₂, LiMnO₂, LiCrO₂, LiMn₂O₄, LiFeO₂, LiFePO₄, andcombinations thereof, wherein each x is independently from 0.4 to 0.6;each y is independently from 0.2 to 0.4; and each z is independentlyfrom 0 to 0.1. In other embodiments, the cathode material is not LiCoO₂,LiNiO₂, LiV₂O₅, LiTiS₂, LiMoS₂, LiMnO₂, LiCrO₂, LiMn₂O₄, LiFeO₂, orLiFePO₄ In further embodiments, the cathode material is notLiNi_(x)Mn_(y)O₂, Li_(1+z)Ni_(x)Mn_(y)Co_(1-x-y)O₂, orLiNi_(x)Co_(y)Al_(z)O₂, wherein each x is independently from 0.3 to 0.8;each y is independently from 0.1 to 0.45; and each z is independentlyfrom 0 to 0.2.

In certain embodiments, the anode material is selected from the groupconsisting of natural graphite particulate, synthetic graphiteparticulate, Sn (tin) particulate, Li₄Ti₅O₁₂ particulate, Si (silicon)particulate, Si—C composite particulate, and combinations thereof. Inother embodiments, the anode material is not natural graphiteparticulate, synthetic graphite particulate, Sn (tin) particulate,Li₄Ti₅O₁₂ particulate, Si (silicon) particulate, or Si—C compositeparticulate.

In some embodiments, the amount of each of the cathode and anodematerials is independently at least 50%, at least 55%, at least 60%, atleast 65%, at least 70%, at least 75%, at least 80%, at least 85%, atleast 90%, or at least 95% by weight, based on the total weight of thecathode or anode electrode layer. In certain embodiments, the amount ofeach of the cathode and anode materials is independently at most 50%, atmost 55%, at most 60%, at most 65%, at most 70%, at most 75%, at most80%, at most 85%, at most 90%, or at most 95% by weight, based on thetotal weight of the cathode or anode electrode layer.

In certain embodiments, the conductive agent is selected from the groupconsisting of carbon, carbon black, graphite, expanded graphite,graphene, graphene nanoplatelets, carbon fibres, carbon nano-fibers,graphitized carbon flake, carbon tubes, carbon nanotubes, activatedcarbon, mesoporous carbon, and combinations thereof. In someembodiments, the conductive agent is not carbon, carbon black, graphite,expanded graphite, graphene, graphene nanoplatelets, carbon fibres,carbon nano-fibers, graphitized carbon flake, carbon tubes, carbonnanotubes, activated carbon, or mesoporous carbon.

In some embodiments, the amount of the conductive agent in each of thecathode and anode electrode layers is independently at least 1%, atleast 2%, at least 3%, at least 4%, at least 5%, at least 10%, at least15%, at least 20%, at least 25%, at least 30%, at least 35%, at least40%, at least 45%, or at least 50% by weight, based on the total weightof the cathode or anode electrode layer. In certain embodiments, theamount of the conductive agent in each of the cathode and anodeelectrode layers is independently at most 1%, at most 2%, at most 3%, atmost 4%, at most 5%, at most 10%, at most 15%, at most 20%, at most 25%,at most 30%, at most 35%, at most 40%, at most 45%, or at most 50% byweight, based on the total weight of the cathode or anode electrodelayer.

In certain embodiments, the amount of the conductive agent in each ofthe cathode and anode electrode layers is independently from about 0.05wt. % to about 0.5 wt. %, from about 0.1 wt. % to about 1 wt. %, fromabout 0.25 wt. % to about 2.5 wt. %, from about 0.5 wt. % to about 5 wt.%, from about 2 wt. % to about 5 wt. %, from about 3 wt. % to about 7wt. %, or from about 5 wt. % to about 10 wt. %, based on the totalweight of the cathode or anode electrode layer.

After assembling the electrode assembly, the electrode assembly isplaced into a drying chamber. In some embodiments, the drying chamber isconnected to a vacuum pump, so that the pressure in the chamber can bereduced. The pressure is reduced sufficiently so as to lower the boilingpoint of water. The drying time can therefore be considerably reduced.In certain embodiments, the drying chamber is connected to a centralvacuum supply, thereby allowing several vacuum drying ovens to beoperated simultaneously. In some embodiments, the number of vacuumdrying ovens connected to a central vacuum supply ranges from 1 to 20depending on the number of pumps operated. In certain embodiments, avacuum pump or central vacuum supply is connected to the drying chamberby a suction line equipped with a gas outlet valve. In some embodiments,the drying chamber is also connected to a gas reservoir containing dryair or inert gas by a duct equipped with a gas inlet valve. When the gasoutlet valve is closed and the gas inlet valve is opened, vacuum is lostin the drying chamber. The valve might be of a solenoid or needle typeor a mass flow controller. Any devices allowing an appropriate flowadjustment might be used.

To reduce the power required for the pumps, a condenser can be providedbetween the drying chamber and the pump. The condenser condenses outwater vapor, which is then separated.

The present invention comprises drying the electrode assembly with atleast two drying stages, namely, the first stage (i.e., step 3) and thesecond stage (i.e., step 4). The electrode assembly disclosed herein isprogressively dried in at least two successive stages, in which thetemperature of the first stage being lower than the temperature in anyof the subsequent stages.

The temperature in the first stage can be within the range of 50° C. to90° C. A partially-dried electrode assembly is obtained from the firststage. In certain embodiments, the electrode assembly can be dried undervacuum in the first stage at a temperature from about 50° C. to about90° C., from about 50° C. to about 85° C., from about 50° C. to about80° C., from about 60° C. to about 90° C., from about 60° C. to about85° C., from about 60° C. to about 80° C., or from about 70° C. to about90° C. In some embodiments, the electrode assembly can be dried undervacuum in the first stage at a temperature of about 50° C. or higher,about 60° C. or higher, about 70° C. or higher, or about 80° C. orhigher. In certain embodiments, the electrode assembly can be driedunder vacuum in the first stage at a temperature of less than 90° C.,less than 85° C., less than 80° C., less than 75° C., less than 70° C.,less than 65° C., less than 60° C., less than 55° C., or less than 50°C.

A lower temperature in the first stage is beneficial to slow drying toavoid crack or embrittlement of the electrode layer. Surface of theelectrode layer should dry out slowly to reduce possibility of surfacecracking since the interior of the electrode layer dries slower than thesurface of the electrode layer.

The drying time for the first stage can be in the range of about 5minute to about 4 hours. In some embodiments, the time period for dryingthe electrode assembly under vacuum in the first stage is from about 5minutes to about 4 hours, from about 5 minutes to about 3 hours, fromabout 5 minutes to about 2 hours, from about 5 minutes to about 1 hour,from about 10 minutes to about 2 hours, from about 15 minutes to about 2hours, from about 15 minutes to about 1 hour, from about 30 minutes toabout 4 hours, from about 30 minutes to about 3 hours, from about 30minutes to about 2 hours, from about 30 minutes to about 1 hour, fromabout 1 hour to about 4 hours, from about 1 hour to about 3 hours, orfrom about 1 hour to about 2 hours. In some embodiments, the time periodfor drying the electrode assembly under vacuum in the first stage isfrom about 5 minutes to about 2 hours, or from about 15 minutes to about30 minutes.

The temperature in the second stage can be within the range of 80° C. to155° C. In certain embodiments, the electrode assembly can be driedunder vacuum in the second stage at a temperature from about 70° C. toabout 155° C., from about 80° C. to about 155° C., from about 90° C. toabout 155° C., from about 100° C. to about 155° C., from about 100° C.to about 140° C., from about 100° C. to about 130° C., from about 100°C. to about 120° C., from about 100° C. to about 110° C., or from about110° C. to about 130° C. In certain embodiments, the electrode assemblycan be dried under vacuum in the second stage at a temperature fromabout 80° C. to about 155° C. In some embodiments, the electrodeassembly can be dried under vacuum in the second stage at a temperatureof about 80° C. or higher, about 90° C. or higher, about 100° C. orhigher, about 110° C. or higher, about 120° C. or higher, about 130° C.or higher, about 140° C. or higher, or about 150° C. or higher. Incertain embodiments, the electrode assembly can be dried under vacuum inthe second stage at a temperature of less than 155° C., less than 150°C., less than 145° C., less than 140° C., less than 135° C., less than130° C., less than 125° C., less than 120° C., less than 115° C., lessthan 110° C., less than 105° C., less than 100° C., or less than 90° C.

The drying time of the second stage can be in the range of about 15minutes to about 4 hours. In some embodiments, the time period fordrying the electrode assembly under vacuum in the second stage is fromabout 15 minutes to about 3 hours, from about 15 minutes to about 2hours, from about 15 minutes to about 1 hour, from about 15 minutes toabout 30 minutes, from about 30 minutes to about 4 hours, from about 30minutes to about 3 hours, from about 30 minutes to about 2 hours, fromabout 30 minutes to about 1 hour, from about 1 hour to about 4 hours,from about 1 hour to about 3 hours, from about 1 hour to about 2 hours,from about 2 hours to about 4 hours, or from about 2 hours to about 3hours. In some embodiments, the time period for drying the electrodeassembly under vacuum in the second stage is from about 5 minutes toabout 2 hours, or from about 15 minutes to about 30 minutes.

Any vacuum pumps that can reduce the pressure of the drying chamber canbe used herein. Some non-limiting examples of the vacuum pumps includedry vacuum pumps, turbo pumps, rotary vane vacuum pumps, cryogenicpumps, and sorption pumps.

In some embodiments, the vacuum pump is an oil free pump. The oil freepump operates without the need for oil in the pump parts which areexposed to gases being pumped, or partial vacuum. Thus, any gasesbackstreaming through the pump are free from oil vapour. Progressive oilvapour deposited on surfaces of the electrode assembly may reduce theelectrochemical performance of a battery. An example of such pump is adiaphragm vacuum pump.

In certain embodiments, high vacuum can be achieved by using a two-stagepumping system to evacuate the drying chamber. The pumping systemcomprises a primary vacuum pump such as a rotary pump or diaphragm pumparranged in series with a high vacuum pump such as a turbo-molecularpump.

In some embodiments, the electrode assembly is dried under atmosphericpressure. In certain embodiments, the drying is performed in a vacuumstate. In further embodiments, the vacuum state is maintained at apressure within the range from about 1×10⁻¹ Pa to about 1×10⁻⁴ Pa, fromabout 10 Pa to about 1×10⁻¹ Pa, from about 1×10³ Pa to about 10 Pa, orfrom about 2.5×10⁴ Pa to about 1×10³ Pa. In still further embodiments,the vacuum state is at a pressure of about 1×10³ Pa, about 2×10³ Pa,about 5×10³ Pa, about 1×10⁴ Pa, or about 2×10⁴ Pa.

After a predetermined drying time period, the drying chamber ventsdirectly to a gas reservoir containing dry air or inert gas via a gasinlet valve. In some embodiments, the gas reservoir is a nitrogen gascylinder. In certain embodiments, the inert gas is selected from thegroup consisting of helium, argon, neon, krypton, xenon, nitrogen,carbon dioxide, and combinations thereof. In some embodiments, the watercontent of the dry air or inert gas is maintained less than or equal to10 ppm, less than or equal to 8 ppm, less than or equal to 5 ppm, lessthan or equal to 4 ppm, less than or equal to 3 ppm, less than or equalto 2 ppm, or less than or equal to 1 ppm.

In certain embodiments, the gas filling step is performed after thesecond drying stage by filling the drying chamber with dry air or inertgas. In other embodiments, the gas filling step is performed after thefirst and second drying stages by filling the drying chamber with dryair or inert gas.

In some embodiments, the dry air or inert gas is preheated beforeentering the drying chamber. In certain embodiments, the temperature ofthe dry air or inert gas is from about 70° C. to about 130° C., fromabout 70° C. to about 110° C., from about 70° C. to about 100° C., fromabout 70° C. to about 90° C., from about 70° C. to about 80° C., fromabout 80° C. to about 155° C., from about 80° C. to about 120° C., fromabout 80° C. to about 100° C., from about 90° C. to about 155° C., fromabout 90° C. to about 130° C., from about 90° C. to about 100° C., fromabout 70° C. to about 155° C., from about 100° C. to about 130° C., orfrom about 100° C. to about 120° C. In some embodiments, the dry air orinert gas is preheated to a temperature from about 70° C. to about 155°C. before entering the drying chamber.

In certain embodiments, the dry air or inert gas stays in the dryingchamber for a time period from about 30 seconds to about 2 hours, fromabout 1 minute to about 1 hour, from about 5 minutes to about 30minutes, from about 5 minutes to about 15 minutes, from about 5 minutesto about 10 minutes, from about 10 minutes to about 30 minutes, fromabout 10 minutes to about 20 minutes, from about 10 minutes to about 15minutes, from about 15 minutes to about 1 hour, from about 15 minutes toabout 30 minutes, from about 15 minutes to about 20 minutes, or fromabout 30 minutes to about 1 hour. In some embodiments, the dry air orinert gas stays in the drying chamber for a time period from about 30seconds to about 2 hours, from about 5 minutes to about 2 hours, or fromabout 15 minutes to about 30 minutes.

In some embodiments, the electrode assembly can be further dried undervacuum after incubating the electrode assembly with the dry gas for apredetermined time. This procedure can be repeated as many times asrequired to reduce the moisture content of the electrode assembly to anappropriate level. In certain embodiments, this procedure can berepeated around 2 to 50 times until the moisture content in theelectrode assembly is less than 40 ppm, less than 30 ppm, less than 20ppm, less than 15 ppm, less than 10 ppm, or less than 5 ppm, based onthe total weight of the dried electrode assembly.

In certain embodiments, the steps of vacuum drying and gas filling canbe repeated at least 2 times, at least 3 times, at least 4 times, atleast 5 times, at least 6 times, at least 7 times, at least 8 times, atleast 9 times, at least 10 times, at least 12 times, at least 14 times,at least 16 times, at least 18 times, at least 20 times, at least 22times, at least 24 times, at least 26 times, at least 28 times, or atleast 30 times. In some embodiments, the steps of vacuum drying and gasfilling can be repeated between 2 and 50 times, between 2 and 30 times,between 2 and 20 times, between 2 and 10 times, between 5 and 30 times,between 5 and 20 times, or between 2 and 10 times. In certainembodiments, the steps of vacuum drying and gas filling can be repeatedbetween 2 or more times.

In some embodiments, the process for drying the electrode assemblycomprises vacuum drying, followed by hot air drying. In someembodiments, the drying chamber blows hot air toward the electrodeassembly from above and/or underneath. In certain embodiments, the hotair drying is performed at an air velocity from about 1 meter/second toabout 50 meters/second, from about 1 meter/second to about 40meters/second, from about 1 meter/second to about 30 meters/second, fromabout 1 meter/second to about 20 meters/second, from about 1meter/second to about 10 meters/second, from about 10 meters/second toabout 50 meters/second, from about 10 meters/second to about 40meters/second, from about 10 meters/second to about 30 meters/second,from about 10 meters/second to about 20 meters/second, from about 20meters/second to about 30 meters/second, from about 30 meters/second toabout 40 meters/second, or from 40 meters/second to about 50meters/second. In other embodiments, a heated inert gas (i.e., helium,argon) is used instead of heated air.

The drying gas might be preheated through heat exchange surfaces. Insome embodiments, the temperature of the hot air ranges from about 50°C. to about 155° C., from about 60° C. to about 150° C., from about 80°C. to about 150° C., from about 100° C. to about 150° C., from about 70°C. to about 150° C., from about 70° C. to about 130° C., from about 70°C. to about 100° C., from about 80° C. to about 150° C., from about 80°C. to about 130° C., from about 80° C. to about 110° C., from about 100°C. to about 140° C., or from about 100° C. to about 120° C.

In certain embodiments, the time period for hot air drying is from about1 minute to about 2 hours, from about 1 minute to about 1 hour, fromabout 1 minute to about 30 minutes, from about 1 minute to about 15minutes, from about 5 minutes to about 30 minutes, from about 5 minutesto about 20 minutes, from about 1 minute to about 15 minutes, from about5 minutes to about 10 minutes, from about 10 minutes to about 1 hour,from about 10 minutes to about 30 minutes, from about 10 minutes toabout 20 minutes, from about 15 minutes to about 1 hour, or from about15 minutes to about 30 minutes.

In some embodiments, the electrode assembly can be further dried undervacuum after blowing hot air for a predetermined time. This procedurecan be repeated as many times as required to reduce the moisture contentof the electrode assembly to an appropriate level, such as 40 ppm, 30ppm, 20 ppm, 15 ppm, 10 ppm, or 5 ppm.

Currently, water is the key factor needed to be strictly controlled inthe organic-based production process of lithium-ion batteries. Theadvantages of the present invention is that most of the fabrication cantake place outside a dry room. In some embodiments, the assemblingprocess can take place outside a dry room or a glove box. In certainembodiments, only the step for filling electrolyte or both the steps fordrying the electrode assembly and filing electrolyte are carried out ina dry room or a glove box. Thus, humidity control in the factory can beavoided, significantly lowering the investment cost.

The presence of moisture is detrimental to the operation of a battery.Generally, water content in the electrode assembly prepared byconventional methods contains an amount of water greater than 100 ppm byweight, based on the total weight of the electrode assembly. Even if theinitial battery performance is acceptable, the rate of deterioration ofthe battery performance may be unacceptable. To be able to achievesufficiently high battery performance, it would therefore beadvantageous to have a low water content in the battery.

The electrode assembly prepared by the method disclosed herein has aparticularly low water content, contributing to reliable performance ofthe lithium-ion batteries. In some embodiments, the water content in thedried electrode assembly is from about 5 ppm to about 50 ppm, from about5 ppm to about 40 ppm, from about 5 ppm to about 30 ppm, from about 5ppm to about 20 ppm, from about 5 ppm to about 10 ppm, from about 3 ppmto about 30 ppm, from about 3 ppm to about 20 ppm, or from about 3 ppmto about 10 ppm by weight, based on the total weight of the driedelectrode assembly.

In certain embodiments, the water content in the dried electrodeassembly is less than 50 ppm, less than 40 ppm, less than 30 ppm, lessthan 20 ppm, less than 10 ppm, less than 5 ppm, less than 4 ppm, lessthan 3 ppm, less than 2 ppm, or less than 1 ppm by weight, based on thetotal weight of the dried electrode assembly. In some embodiments, thedried electrode assembly disclosed herein has a water concentrationtherein no greater than about 5 ppm by weight, based on the total weightof the dried electrode assembly.

In some embodiments, the dried electrode assembly comprises at least onedried anode and at least one dried cathode, wherein the at least onedried anode and at least one dried cathode have a water content of lessthan 50 ppm, less than 40 ppm, less than 30 ppm, less than 20 ppm, lessthan 10 ppm, less than 5 ppm, or less than 3 ppm by weight, based on thetotal weight of the at least one dried anode and at least one driedcathode.

In certain embodiments, the at least one anode and at least one cathodehave a water content of less than 30 ppm, less than 20 ppm, less than 10ppm, or less than 5 ppm by weight, based on the total weight of the atleast one anode and at least one cathode. In some embodiments, the atleast one cathode or anode has a water content of less than 30 ppm, lessthan 20 ppm, less than 15 ppm, less than 10 ppm, less than 5 ppm, lessthan 4 ppm, less than 3 ppm, less than 2 ppm, or less than 1 ppm byweight, based on the total weight of the at least one cathode or anode.

In some embodiments, the dried electrode assembly comprises at least onedried separator, wherein the at least one dried separator has a watercontent of less than 50 ppm, less than 40 ppm, less than 30 ppm, lessthan 20 ppm, less than 10 ppm, less than 5 ppm, or less than 3 ppm byweight, based on the total weight of the at least one dried separator.

The peeling strength of the electrode coating layer has beenconventionally increased by increasing the amount of binder in thecoating layer. However, increase in the amount of binder naturally leadsto decrease in the amount of the electrode active material in theelectrode coating layer, thereby decreasing the battery capacity perunit weight. By performing a two-stage drying process, a practicallysufficient peeling strength is obtained.

The present invention comprises drying the electrode assembly with twodrying stages, the first stage and the second stage, in which thetemperature of the first stage is lower than the temperature of thesecond stage. A lower temperature in the first stage prevents rapid lossof surface moisture and increases product quality by virtuallyeliminating non-uniformity in drying. If drying is too rapid or thetemperature is too high, this can cause uneven drying and may make theelectrode layer to shrink unevenly, thereby causing a reduction inelectrode peeling strength.

No prior art document discloses a drying method that describes therelation between a binder composition and an electrode peeling strength.The two-stage drying process is particularly suitable for electrodescomprising aqueous binders. Binders make up only a small part of theelectrode composition, but in some cases, they play an important role inaffecting the battery performance such as cycling stability and ratecapability of lithium-ion batteries. Aqueous binders are greener andeasier to be used for electrode fabrication. However, water-based bindersuch as carboxymethyl cellulose (CMC) is considered a brittle binder,which breaks after little deformation. If drying is too rapid or thetemperature is too high, the aqueous binder is likely to become brittle,resulting in a brittle electrode.

In some embodiments, the at least one cathode comprises a cathodecurrent collector and a cathode electrode layer, wherein the peelingstrength between the cathode current collector and the cathode electrodelayer is 0.05 N/cm or more, 0.1 N/cm or more, 0.15 N/cm or more, 0.2N/cm or more, 0.25 N/cm or more, 0.3 N/cm or more, 0.35 N/cm or more,0.4 N/cm or more, 0.5 N/cm or more, or 0.75 N/cm or more. In certainembodiments, the peeling strength between the cathode electrode layerand the cathode current collector is between 0.05 N/cm and 0.75 N/cm,between 0.05 N/cm and 0.6 N/cm, between 0.05 N/cm and 0.5 N/cm, between0.1 N/cm and 0.5 N/cm, between 0.1 N/cm and 0.45 N/cm, between 0.1 N/cmand 0.4 N/cm, between 0.1 N/cm and 0.35 N/cm, between 0.15 N/cm and 0.5N/cm, between 0.15 N/cm and 0.45 N/cm, between 0.15 N/cm and 0.4 N/cm,between 0.15 N/cm and 0.35 N/cm, or between 0.15 N/cm and 0.3 N/cm.

In certain embodiments, the at least one anode comprises an anodecurrent collector and an anode electrode layer, wherein the peelingstrength between the anode current collector and the anode electrodelayer is 0.05 N/cm or more, 0.1 N/cm or more, 0.15 N/cm or more, 0.2N/cm or more, 0.3 N/cm or more, 0.35 N/cm or more, 0.45 N/cm or more,0.5 N/cm or more, 0.55 N/cm or more, or 0.65 N/cm or more. In someembodiments, the peeling strength between the anode electrode layer andthe anode current collector is between 0.05 N/cm and 0.65 N/cm, between0.05 N/cm and 0.45 N/cm, between 0.05 N/cm and 0.4 N/cm, between 0.1N/cm and 0.55 N/cm, between 0.1 N/cm and 0.45 N/cm, between 0.1 N/cm and0.4 N/cm, between 0.1 N/cm and 0.35 N/cm, between 0.15 N/cm and 0.5N/cm, between 0.15 N/cm and 0.45 N/cm, between 0.15 N/cm and 0.4 N/cm,between 0.15 N/cm and 0.35 N/cm, or between 0.15 N/cm and 0.3 N/cm.

Detachment of the active material is less likely to occur duringrepetitive charging and discharging when the peeling strength betweenthe current collector and the electrode layer is high. In the case wherethe electrode peeling strength is 0.15 N/cm or more, the electrode hassufficient peeling strength after lamination of the active electrodematerial onto a surface of the current collector and the electrode layerdoes not separate during volume change due to shrinkage and expansion ofthe electrode active material during charging and discharging of arechargeable lithium battery.

After the drying step, the electrode assembly can then be naturallycooled to 50° C. or less before being removed from the drying chamber.In some embodiments, the electrode assembly is cooled to 45° C. or less,40° C. or less, 35° C. or less, 30° C. or less, or 25° C. or less beforebeing removed from the drying chamber. In certain embodiments, theelectrode assembly is cooled to room temperature. In some embodiments,the electrode assembly is cooled down by blowing a dry gas or inert gasin order to reach the target temperature more quickly.

The binder material in the electrode layer performs a role of bindingthe electrode material and conductive agent together on the currentcollector. In certain embodiments, each of the at least one anode and atleast one cathode independently comprises a binder material selectedfrom the group consisting of an organic-based binder material, awater-based binder material, or a mixture of water-based andorganic-based binder materials.

In some embodiments, each of the binder materials in the cathode andanode electrode layers is independently selected from the groupconsisting of styrene-butadiene rubber, acrylated styrene-butadienerubber, acrylonitrile copolymer, acrylonitrile-butadiene rubber, nitrilebutadiene rubber, acrylonitrile-styrene-butadiene copolymer, acrylrubber, butyl rubber, fluorine rubber, polytetrafluoroethylene,polyethylene, polypropylene, ethylene/propylene copolymers,polybutadiene, polyethylene oxide, chlorosulfonated polyethylene,polyvinylpyrrolidone, polyvinylpyridine, polyvinyl alcohol, polyvinylacetate, polyepichlorohydrin, polyphosphazene, polyacrylonitrile,polystyrene, latex, acrylic resins, phenolic resins, epoxy resins,carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate,cellulose acetate butyrate, cellulose acetate propionate,cyanoethylcellulose, cyanoethylsucrose, polyester, polyamide, polyether,polyimide, polycarboxylate, polycarboxylic acid, polyacrylic acid,polyacrylate, polymethacrylic acid, polymethacrylate, polyacrylamide,polyurethane, fluorinated polymer, chlorinated polymer, a salt ofalginic acid, polyvinylidene fluoride, poly(vinylidenefluoride)-hexafluoropropene, and combinations thereof. In furtherembodiments, the salt of alginic acid comprises a cation selected fromNa, Li, K, Ca, NH₄, Mg, Al, or a combination thereof.

In certain embodiments, each of the binder materials in the cathode andanode electrode layers is independently selected from the groupconsisting of styrene-butadiene rubber, carboxymethyl cellulose,polyvinylidene fluoride, acrylonitrile copolymer, polyacrylic acid,polyacrylonitrile, poly(vinylidene fluoride)-hexafluoropropene, latex, asalt of alginic acid, and combinations thereof.

In some embodiments, each of the binder materials in the cathode andanode electrode layers is independently selected from SBR, CMC, PAA, asalt of alginic acid, or a combination thereof. In certain embodiments,each of the binder materials in the cathode and anode electrode layersis independently acrylonitrile copolymer. In some embodiments, each ofthe binder materials in the cathode and anode electrode layers isindependently polyacrylonitrile. In certain embodiments, each of thebinder materials in the cathode and anode electrode layers independentlyis free of styrene-butadiene rubber, carboxymethyl cellulose,polyvinylidene fluoride, acrylonitrile copolymer, polyacrylic acid,polyacrylonitrile, poly(vinylidene fluoride)-hexafluoropropene, latex,or a salt of alginic acid.

In certain embodiments, the amount of the binder material in each of thecathode and anode electrode layers is independently at least 1%, atleast 2%, at least 3%, at least 4%, at least 5%, at least 10%, at least15%, at least 20%, at least 25%, at least 30%, at least 35%, at least40%, at least 45%, or at least 50% by weight, based on the total weightof the cathode or anode electrode layer. In some embodiments, the amountof the binder material in each of the cathode and anode electrode layersis independently at most 1%, at most 2%, at most 3%, at most 4%, at most5%, at most 10%, at most 15%, at most 20%, at most 25%, at most 30%, atmost 35%, at most 40%, at most 45%, or at most 50% by weight, based onthe total weight of the cathode or anode electrode layer.

In some embodiments, the amount of the binder material in each of thecathode and anode electrode layers is independently is from about 2 wt.% to about 10 wt. %, from about 3 wt. % to about 6 wt. %, from about 5wt. % to about 10 wt. %, from about 7.5 wt. % to about 15 wt. %, fromabout 10 wt. % to about 20 wt. %, from about 15 wt. % to about 25 wt. %,from about 20 wt. % to about 40 wt. %, or from about 35 wt. % to about50 wt. %, based on the total weight of the cathode or anode electrodelayer.

In order to prevent moisture from being present within the sealedcontainer, the step of filling electrolyte is carried out in a dry room.After drying, the electrode assembly is placed inside a container andthen an electrolyte is added to fill the pores of all of the layers ofseparator and electrodes, and each of the gaps between the positive andnegative electrodes and the separator in the electrode assembly under aninert atmosphere before sealing.

The method disclosed herein reduces the production costs of lithium-ionbatteries by consuming less energy and shortens manufacturing timesneeded for drying. Therefore, this method is especially suited forindustrial processes because of its low cost and ease of handling.

Also provided herein is a lithium battery comprising the electrodeassembly prepared by the method disclosed herein.

The following examples are presented to exemplify embodiments of theinvention. All numerical values are approximate. When numerical rangesare given, it should be understood that embodiments outside the statedranges may still fall within the scope of the invention. Specificdetails described in each example should not be construed as necessaryfeatures of the invention.

EXAMPLES

The water content in the electrode assembly was measured by Karl-fishertitration. The electrode assembly was cut into small pieces of 1 cm×1 cmin a glove box filled with argon gas. The cut electrode assembly havinga size of 1 cm×1 cm was weighed in a sample vial. The weighed electrodeassembly was then added into a titration vessel for Karl Fischertitration using Karl Fischer coulometry moisture analyzer (831 KFCoulometer, Metrohm, Switzerland). Measurements were repeated threetimes to find the average value.

The water content in the electrodes or separator was measured byKarl-fisher titration. The electrode assembly was cut into small piecesof 1 cm×1 cm in a glove box filled with argon gas. The electrodeassembly was separated into the anode, cathode and separator layers. Thewater contents of the separated electrode layers and separator layerswere analysed separately by Karl Fischer titration. Measurements wererepeated three times to find the average value.

The peeling strengths of the electrodes were measured by a peelingtester (obtained from Instron, US; model no. MTS 5581). The driedelectrode assembly was separated into the anode, cathode and separatorlayers. Each of the cathode and anode layers was cut into a rectangularshape having a size of 25 mm×100 mm. Then, a strip of mending tape (3M;US; model no. 810) was attached onto the electrode surface having theelectrode coating layer, and then pressed by a reciprocating movement ofa 2 kg roller thereon to prepare samples for peeling strength test. Eachof the samples was mounted on the peeling tester, followed bymeasurement of the peeling strength by peeling off the mending tape at180° at room temperature. The mending tape was peeled off at a rate of50 mm/minute. Measurements were taken at a predetermined interval of 10mm to 70 mm and were repeated 3 times.

Example 1 A) Preparation of Positive Electrode Slurry

A positive electrode slurry was prepared by mixing 94 wt. % cathodematerial (LNMC TLM 310, obtained from Xinxiang Tianli Energy Co. Ltd.,China), 3 wt. % carbon black (SuperP; obtained from Timcal Ltd, Bodio,Switzerland) as a conductive agent, and 0.8 wt. % polyacrylic acid (PAA,#181285, obtained from Sigma-Aldrich, US), 1.5 wt. % styrene butadienerubber (SBR, AL-2001, obtained from NIPPON A&L INC., Japan) and 0.7 wt.% polyvinylidene fluoride (PVDF; Solef® 5130, obtained from Solvay S.A.,Belgium) as a binder, which were dispersed in deionized water to form aslurry with a solid content of 50 wt. %. The slurry was homogenized by aplanetary stirring mixer.

B) Preparation of Positive Electrode

The homogenized slurry was coated onto both sides of an aluminum foilhaving a thickness of 20 μm and a surface roughness Ra of 1.2 μm using atransfer coater (ZY-TSF6-6518, obtained from Jin Fan Zhanyu New EnergyTechnology Co. Ltd., China) with an area density of about 26 mg/cm². Thecoated films on the aluminum foil were dried for 3 minutes by a24-meter-long conveyor hot air drying oven as a sub-module of thetransfer coater operated at a conveyor speed of about 8 meters/minute toobtain a positive electrode. The temperature-programmed oven allowed acontrollable temperature gradient in which the temperature graduallyrose from the inlet temperature of 60° C. to the outlet temperature of75° C. The electrode was then pressed to increase the density of thecoating and the density was 2.74 g/cm³. The void volume of the electrodelayer is 31%.

C) Preparation of Negative Electrode

A negative electrode slurry was prepared by mixing 90 wt. % hard carbon(HC; 99.5% purity, Ruifute Technology Ltd., Shenzhen, Guangdong, China),5 wt. % carbon black and 5 wt. % polyacrylonitrile in deionized water toform a slurry having a solid content of 50 wt. %. The slurry was coatedonto both sides of a copper foil having a thickness of 9 μm and asurface roughness Ra of 0.7 μm using a transfer coater with an areadensity of about 15 mg/cm². The coated films on the copper foil weredried at about 50° C. for 2.4 minute by a 24-meter-long conveyor hot airdryer operated at a conveyor speed of about 10 meters/minute to obtain anegative electrode. The electrode was then pressed to increase thedensity of the coating and the density was 1.8 g/cm³. The void volume ofthe electrode layer is 19%.

Example 2 Assembling of Electrode Assembly

After drying, the resulting cathode film and anode film of Example 1were used to prepare the cathode and anode respectively by cutting intoindividual electrode plates. An electrode assembly was prepared bystacking anodes, cathodes and separators interposed between the positiveelectrode and the negative electrode in the open air with no control ofhumidity. The separator was a microporous membrane made of nonwoven PETfabric (obtained from MITSUBISHI PAPER MILLS LTD, Japan), which had athickness of 30 μm. The electrode assembly was dried in a vacuum oveninside a glove box under a pressure of 5×10³ Pa at 70° C. for 2.5 hoursduring the first stage of drying. The electrode assembly was furtherdried under vacuum at 5×10³ Pa at 120° C. for 1.5 hours during thesecond stage of drying. The drying chamber was then filled with hot, dryair having a water content of 5 ppm and a temperature of 90° C. The hot,dry air was retained in the drying chamber for 15 minutes beforeevacuating the drying chamber. The cycle involving the steps of vacuumdrying in the second stage and gas filling performed after the secondstage was repeated 10 times.

Moisture Contents of Electrode Assembly, Electrodes and Separator

The average values of moisture contents of the electrode assembly,electrodes and separator were 5 ppm, 9 ppm and 13 ppm respectively.

Electrode Peeling Strengths

The average values of peeling strengths of the processed cathode andanode in the dried electrode assembly were 0.45 N/cm and 0.23 N/cmrespectively, and the average values of peeling strengths of theunprocessed cathode and anode were 0.44 N/cm and 0.21 N/cm respectively.Both the cathode and anode showed high peeling strengths which remainedlargely unaffected by the drying processes.

Assembling of Pouch-Type Battery

A pouch cell was assembled by packaging the dried electrode assembly ina case made of an aluminum-plastic laminated film. The cathode and anodeelectrode plates were kept apart by separators and the case waspre-formed. An electrolyte was then filled into the case holding thepacked electrodes in high-purity argon atmosphere with moisture andoxygen content <1 ppm. The electrolyte was a solution of LiPF₆ (1 M) ina mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC) anddimethyl carbonate (DMC) in a volume ratio of 1:1:1. After electrolytefilling, the pouch cells were vacuum sealed and then mechanicallypressed using a punch tooling with standard square shape.

Electrochemical Measurements of Example 2

I) Nominal Capacity

The cell was tested galvanostatically at a current density of C/2 at 25°C. on a battery tester (BTS-5V20A, obtained from Neware Electronics Co.Ltd, China) between 3.0 V and 4.2 V. The nominal capacity was about 2.8Ah.

II) Cyclability Performance

The cyclability performance of the pouch cell was tested by charging anddischarging at a constant current rate of 1 C between 3.0 V and 4.2 V.Test result of cyclability performance is shown in FIG. 1. The capacityretention after 562 cycles was about 94.7% of the initial value. Theelectrochemical tests show good electrochemical stability of the batteryin a wide range of potential, as well as outstanding cycle performance.

Example 3 A) Preparation of Positive Electrode Slurry

A positive electrode slurry was prepared by mixing 92 wt. % cathodematerial (LiMn₂O₄ obtained from HuaGuan HengYuan LiTech Co. Ltd.,Qingdao, China), 4 wt. % carbon black (SuperP; obtained from Timcal Ltd,Bodio, Switzerland) as a conductive agent, and 4 wt. % polyvinylidenefluoride (PVDF; Solef® 5130, obtained from Solvay S.A., Belgium) as abinder, which were dispersed in N-methyl-2-pyrrolidone (NMP; purityof >99%, Sigma-Aldrich, USA) to form a slurry with a solid content of 50wt. %. The slurry was homogenized by a planetary stirring mixer.

B) Preparation of Positive Electrode

The homogenized slurry was coated onto both sides of an aluminum foilhaving a thickness of 20 μm using a transfer coater with an area densityof about 2.4 mg/cm². The coated films on the aluminum foil were driedfor 6 minutes by a 24-meter-long conveyor hot air drying oven as asub-module of the transfer coater operated at a conveyor speed of about4 meters/minute to obtain a positive electrode. Thetemperature-programmed oven allowed a controllable temperature gradientin which the temperature gradually rose from the inlet temperature of65° C. to the outlet temperature of 80° C. The electrode was thenpressed to increase the density of the coating and the density was 2.83g/cm³. The void volume of the electrode layer is 29%.

C) Preparation of Negative Electrode

A negative electrode slurry was prepared by mixing 90 wt. % of hardcarbon (HC; purity of 99.5%, obtained from Ruifute Technology Ltd.,Shenzhen, Guangdong, China) with 1.5 wt. % carboxymethyl cellulose (CMC,BSH-12, DKS Co. Ltd., Japan) and 3.5 wt. % SBR (AL-2001, NIPPON A&LINC., Japan) as a binder, and 5 wt. % carbon black as a conductiveagent, which were dispersed in deionized water to form another slurrywith a solid content of 50 wt. %. The slurry was coated onto both sidesof a copper foil having a thickness of 9μm using a transfer coater withan area density of about 15 mg/cm². The coated films on the copper foilwere dried at about 50° C. for 2.4 minutes by a 24-meter-long conveyorhot air dryer operated at a conveyor speed of about 10 meters/minute toobtain a negative electrode. The electrode was then pressed to increasethe density of the coating and the density was 1.8 g/cm³. The voidvolume of the electrode layer is 19%.

Example 4 Assembling of Electrode Assembly

After drying, the resulting cathode film and anode film of Example 3were used to prepare the cathode and anode respectively by cutting intoindividual electrode plates. An electrode assembly was prepared bystacking anodes, cathodes and separators interposed between the positiveelectrode and the negative electrode in the open air with no control ofhumidity. The separator was a ceramic coated microporous membrane madeof nonwoven fabric (SEPARION, Evonik Industries, Germany) having athickness of 35 μm. The electrode assembly was dried in a vacuum oveninside a glove box under a pressure of 1×10⁴ Pa at 85° C. for 1.5 hoursduring the first stage of drying. The electrode assembly was furtherdried under vacuum at 5×10³ Pa at 105° C. for 2.5 hours during thesecond stage of drying. The drying chamber was then filled with hot, dryair having a water content of 5 ppm and a temperature of 90° C. The hot,dry air was retained in the drying chamber for 15 minutes beforeevacuating the drying chamber. The cycle involving the steps of vacuumdrying in the second stage and gas filling performed after the secondstage was repeated 5 times.

Moisture Contents of Electrode Assembly, Electrodes and Separator

The average values of moisture contents of the electrode assembly,electrodes and separator were 13 ppm, 9 ppm and 15 ppm respectively.

Electrode Peeling Strengths

The average values of peeling strengths of the processed cathode andanode in the dried electrode assembly were 0.31 N/cm and 0.18 N/cmrespectively, and the average values of peeling strengths of theunprocessed cathode and anode were 0.32 N/cm and 0.17 N/cm respectively.Both the cathode and anode showed high peeling strengths which remainedlargely unaffected by the drying processes.

Electrochemical Measurements of Example 4 I) Nominal Capacity

A pouch cell containing the dried electrode assembly prepared by methoddescribed in Example 4 was assembled according to the method describedin Example 2. The cell was tested galvanostatically at a current densityof C/2 at 25° C. on a battery tester between 3.0 V and 4.2 V. Thenominal capacity was about 2.9 Ah.

II) Cyclability Performance

The cyclability performance of the pouch cell was tested by charging anddischarging at a constant current rate of 1 C between 3.0 V and 4.2 V.Test result of cyclability performance is shown in FIG. 2. The capacityretention after 1050 cycles was about 94.2% of the initial value. Theelectrochemical tests show the good electrochemical stability of thebattery in a wide range of potential, as well as outstanding cycleperformance.

Example 5 A) Preparation of Positive Electrode Slurry

A positive electrode slurry was prepared by mixing 94 wt. % cathodematerial LiNi_(0.33)Mn_(0.33)Co_(0.33)O₂ (obtained from ShenzhenTianjiao Technology Co. Ltd., China), 3 wt. % carbon black (SuperP;obtained from Timcal Ltd, Bodio, Switzerland) as a conductive agent, and1.5 wt. % polyacrylic acid (PAA, #181285, obtained from Sigma-Aldrich,US) and 1.5 wt. % polyacrylonitrile (LA 132, Chengdu Indigo PowerSources Co., Ltd., China) as a binder, which were dispersed in deionizedwater to form a slurry with a solid content of 50 wt. %. The slurry washomogenized by a planetary stirring mixer.

B) Preparation of Positive Electrode

The homogenized slurry was coated onto both sides of an aluminum foilhaving a thickness of 20 μm using a transfer coater with an area densityof about 32 mg/cm². The coated films on the aluminum foil were dried for4 minutes by a 24-meter-long conveyor hot air drying oven as asub-module of the transfer coater operated at a conveyor speed of about6 meters/minute to obtain a positive electrode. Thetemperature-programmed oven allowed a controllable temperature gradientin which the temperature gradually rose from the inlet temperature of60° C. to the outlet temperature of 75° C. The electrode was thenpressed to increase the density of the coating and the density was 3.47g/cm³. The void volume of the electrode layer is 13%.

C) Preparation of Negative Electrode

A negative electrode slurry was prepared by mixing 90 wt. % hard carbon,5 wt. % carbon black and 5 wt. % polyacrylonitrile in deionized water toform a slurry having a solid content of 50 wt. %. The slurry was coatedonto both sides of a copper foil having a thickness of 9 μm using atransfer coater with an area density of about 15 mg/cm². The coatedfilms on the copper foil were dried at about 50° C. for 2.4 minutes by a24-meter-long conveyor hot air dryer operated at a conveyor speed ofabout 10 meters/minute to obtain a negative electrode.

Example 6 Assembling of Electrode Assembly

After drying, the resulting cathode film and anode film of Example 5were used to prepare the cathode and anode respectively by cutting intoindividual electrode plates. An electrode assembly was prepared bystacking anodes, cathodes and separators interposed between the positiveelectrode and the negative electrode in the open air with no control ofhumidity. The separator was a microporous membrane made of polyimide(Jiangxi Advanced Nanofiber Technology Co., Ltd., China) having athickness of 20 μm. The electrode assembly was dried in a vacuum oveninside a glove box under a pressure of 1.5×10⁴ Pa at 95° C. for 3.5hours during the first stage of drying. The electrode assembly wasfurther dried under vacuum at 5×10³ Pa at 115° C. for 2 hours during thesecond stage of drying. The drying chamber was then filled with hot, dryair having a water content of 5 ppm and a temperature of 85° C. The hot,dry air was retained in the drying chamber for 15 minutes beforeevacuating the drying chamber. The cycle involving the steps of vacuumdrying in the second stage and gas filling performed after the secondstage was repeated 11 times.

Moisture Content of Electrode Assembly

The average value of moisture content of the electrode assembly was 6ppm.

Electrode Peeling Strengths

The average values of peeling strengths of the processed cathode andanode in the dried electrode assembly were 0.51 N/cm and 0.28 N/cmrespectively, and the average values of peeling strengths of theunprocessed cathode and anode were 0.49 N/cm and 0.25 N/cm respectively.Both the cathode and anode showed high peeling strengths which remainedlargely unaffected by the drying processes.

Electrochemical Measurements of Example 6 I) Nominal Capacity

A pouch cell containing the dried electrode assembly prepared by methoddescribed in Example 6 was assembled according to the method describedin Example 2. The cell was tested galvanostatically at a current densityof C/2 at 25° C. on a battery tester between 3.0 V and 4.2 V. Thenominal capacity was about 10 Ah.

II) Cyclability Performance

The cyclability performance of the pouch cell was tested by charging anddischarging at a constant current rate of 1 C between 3.0 V and 4.2 V.Test result of cyclability performance is shown in FIG. 3. The capacityretention after 601 cycles was about 94.3% of the initial value. Theelectrochemical tests show the good electrochemical stability of thebattery in a wide range of potential, as well as outstanding cycleperformance.

Example 7 A) Preparation of Positive Electrode Slurry

A positive electrode slurry was prepared by mixing 91 wt. % cathodematerial LiFePO₄ (obtained from Xiamen Tungsten Co. Ltd., China), 5 wt.% carbon black (SuperP; obtained from Timcal Ltd, Bodio, Switzerland) asa conductive agent, and 4 wt. % polyacrylonitrile (LA 132, ChengduIndigo Power Sources Co., Ltd., China) as a binder, which were dispersedin deionized water to form a slurry with a solid content of 50 wt. %.The slurry was homogenized by a planetary stirring mixer.

B) Preparation of Positive Electrode

The homogenized slurry was coated onto both sides of an aluminum foilhaving a thickness of 30 μm using a transfer coater with an area densityof about 56 mg/cm². The coated films on the aluminum foil were thendried for 6 minutes by a 24-meter-long conveyor hot air drying oven as asub-module of the transfer coater operated at a conveyor speed of about4 meters/minute to obtain a positive electrode. Thetemperature-programmed oven allowed a controllable temperature gradientin which the temperature gradually rose from the inlet temperature of75° C. to the outlet temperature of 90° C. The electrode was thenpressed to increase the density of the coating and the density was 2.98g/cm³. The void volume of the electrode layer is 26%.

C) Preparation of Negative Electrode

A negative electrodes were prepared by mixing 90 wt. % of hard carbon(HC; purity of 99.5%, obtained from Ruifute Technology Ltd., China) with1.5 wt. % CMC (BSH-12, DKS Co. Ltd., Japan) and 3.5 wt. % SBR (AL-2001,NIPPON A&L INC., Japan) as a binder, and 5 wt. % carbon black as aconductive agent, which were dispersed in deionized water to formanother slurry with a solid content of 50 wt. %. The slurry was coatedonto both sides of a copper foil having a thickness of 9 μm using atransfer coater with an area density of about 15 mg/cm². The coatedfilms on the copper foil were then dried at about 50° C. for 2.4 minutesby a 24-meter-long conveyor hot air dryer operated at a conveyor speedof about 10 meters/minute to obtain a negative electrode.

Example 8 Assembling of Electrode Assembly

After drying, the resulting cathode film and anode film of Example 7were used to prepare the cathode and anode respectively by cutting intoindividual electrode plates. An electrode assembly was prepared bystacking anodes, cathodes and separators interposed between the positiveelectrode and the negative electrode in the open air with no control ofhumidity. The separator was a ceramic coated microporous membrane madeof nonwoven fabric (SEPARION, Evonik Industries, Germany), which had athickness of about 35 μm. The electrode assembly was dried in a vacuumoven inside a glove box under a pressure of 7×10³ Pa at 65° C. for 4hours. The electrode assembly was further dried under vacuum at 1×10⁴ Paat 115° C. for 1.2 hours. The drying chamber was then filled with hot,dry air having a water content of 5 ppm and a temperature of 100° C. Thehot, dry air was retained in the drying chamber for 5 minutes beforeevacuating the drying chamber. The cycle involving the steps of vacuumdrying in the second stage and gas filling performed after the secondstage was repeated 8 times.

Moisture Content of Electrode Assembly

The average value of moisture content of the electrode assembly was 7ppm.

Electrode Peeling Strengths

The average values of peeling strengths of the processed cathode andanode in the dried electrode assembly were 0.38 N/cm and 0.24 N/cmrespectively, and the average values of peeling strengths of theunprocessed cathode and anode were 0.37 N/cm and 0.22 N/cm respectively.Both the cathode and anode showed high peeling strengths which remainedlargely unaffected by the drying processes.

Electrochemical Measurements of Example 8 I) Nominal Capacity

A pouch cell containing the dried electrode assembly prepared by methoddescribed in Example 8 was assembled according to the method describedin Example 2. The cell was tested galvanostatically at a current densityof C/2 at 25° C. on a battery tester between 3.0 V and 4.2 V. Thenominal capacity was about 9 Ah.

II) Cyclability Performance

The cyclability performance of the pouch cell was tested by charging anddischarging at a constant current rate of 1 C between 3.0 V and 4.2 V.Test result of cyclability performance is shown in FIG. 4. The capacityretention after 452 cycles was about 94.2% of the initial value. Theelectrochemical tests show the good electrochemical stability of thebattery in a wide range of potential, as well as outstanding cycleperformance.

While the invention has been described with respect to a limited numberof embodiments, the specific features of one embodiment should not beattributed to other embodiments of the invention. Variations andmodifications from the described embodiments exist. The appended claimsintend to cover all those modifications and variations as falling withinthe scope of the invention.

What is claimed is:
 1. An electrode for a lithium-ion battery,comprising a current collector and an electrode layer, wherein thecurrent collector is in the form of a foil, sheet, or film, wherein theelectrode layer has a void volume between 10% and 35%, and wherein theelectrode has a peeling strength between 0.15 N/cm and 0.31 N/cm.
 2. Theelectrode of claim 1, wherein the surface roughness of the currentcollector is 4 μm or less.
 3. The electrode of claim 1, wherein thedensity of the electrode layer is from about 1.0 g/cm³ to about 6.5g/cm³.
 4. The electrode of claim 1, wherein the density of the electrodelayer is from about 1.0 g/cm³ to about 3.0 g/cm³.
 5. The electrode ofclaim 1, wherein the thickness of the electrode layer is from about 1.0μm to about 40 μm.
 6. The electrode of claim 1, wherein the thickness ofthe electrode layer is from about 1.0 μm to about 25 μm.
 7. Theelectrode of claim 1, wherein the electrode layer comprises a cathodematerial or an anode material, a binder material and a conductive agent,and wherein the binder material in the electrode layer is selected fromthe group consisting of styrene-butadiene rubber, acrylatedstyrene-butadiene rubber, acrylonitrile copolymer,acrylonitrile-butadiene rubber, nitrile butadiene rubber,acrylonitrile-styrene-butadiene copolymer, acryl rubber, butyl rubber,fluorine rubber, polytetrafluoroethylene, polyethylene, polypropylene,ethylene/propylene copolymers, polybutadiene, polyethylene oxide,chlorosulfonated polyethylene, polyvinylpyrrolidone, polyvinylpyridine,polyvinyl alcohol, polyvinyl acetate, polyepichlorohydrin,polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resins,phenolic resins, epoxy resins, carboxymethyl cellulose, hydroxypropylcellulose, cellulose acetate, cellulose acetate butyrate, celluloseacetate propionate, cyanoethylcellulose, cyanoethylsucrose, polyester,polyamide, polyether, polyimide, polycarboxylate, polycarboxylic acid,polyacrylic acid, polyacrylate, polymethacrylic acid, polymethacrylate,polyacrylamide, polyurethane, fluorinated polymer, chlorinated polymer,a salt of alginic acid, polyvinylidene fluoride, poly(vinylidenefluoride)-hexafluoropropene, and combinations thereof.
 8. The electrodeof claim 7, wherein the binder material in the electrode layer ispresent in an amount from 2% to 10% by weight, based on the total weightof the electrode layer.
 9. The electrode of claim 7, wherein the cathodematerial is selected from the group consisting of LiCoO₂, LiNiO₂,LiNi_(x)Mn_(y)O₂, Li_(1+z)Ni_(x)Mn_(y)Co_(1-x-y)O₂,LiNi_(x)Co_(y)Al_(z)O₂, LiV₂O₅, LiTiS₂, LiMoS₂, LiMnO₂, LiCrO₂, LiMn₂O₄,LiFeO₂, LiFePO₄, and combinations thereof, wherein each x isindependently from 0.3 to 0.8; each y is independently from 0.1 to 0.45;and each z is independently from 0 to 0.2.
 10. The electrode of claim 9,wherein the cathode material is present in an amount from 60% to 99% byweight, based on the total weight of the electrode layer.
 11. Theelectrode of claim 7, wherein the conductive agent in the electrodelayer is selected from the group consisting of carbon, carbon black,graphite, expanded graphite, graphene, graphene nanoplatelets, carbonfibres, carbon nano-fibers, graphitized carbon flake, carbon tubes,carbon nanotubes, activated carbon, mesoporous carbon, and combinationsthereof.
 12. The electrode of claim 11, wherein the conductive agent inthe electrode layer is present in an amount from 2% to 10% by weight,based on the total weight of the electrode layer.
 13. The electrode ofclaim 7, wherein the anode material is selected from the groupconsisting of natural graphite particulate, synthetic graphiteparticulate, Sn particulate, Li₄Ti₅O₁₂ particulate, Si particulate, Si—Ccomposite particulate, and combinations thereof.
 14. The electrode ofclaim 13, wherein the anode material is present in an amount from 50% to99% by weight, based on the total weight of the electrode layer.
 15. Theelectrode of claim 1, wherein the current collector is stainless steel,titanium, nickel, aluminum, copper, or electrically-conductive resin.16. The electrode of claim 1, wherein the electrode is a cathode and thecurrent collector is an aluminum thin film.
 17. The electrode of claim1, wherein the electrode is an anode and the current collector is acopper thin film.
 18. The electrode of claim 1, wherein the electrodehas a water content of less than 20 ppm, based on the total weight ofthe electrode.
 19. The electrode of claim 1, wherein the electrode has awater content of less than 10 ppm, based on the total weight of theelectrode.
 20. A lithium battery comprising the electrode of claim 1.